Inkjet recording apparatus

ABSTRACT

Plural unit heads are disposed in a paper conveyance direction, and recording head units are configured and disposed in a staggered manner. Head recovery devices are disposed as positions avoiding the locus of splattering of ink droplets from the unit heads. The recording head units can record an image across the entire width of a sheet of paper, and it is not necessary to move the recording head units in the paper width direction. Dummy jetting can be conducted at gap regions between two sheets of paper in an image recording section. The plural unit heads are unitized.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese PatentApplication No. 2003-328422, the disclosure of which is incorporated byreference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inkjet recording apparatus, and inparticular to a recording apparatus used as an output device, such as anink-jet recording apparatus that conducts recording by discharging inkdroplets onto a recording medium, and a fax machine, a copier, a printercomposite device and a workstation disposed with such a function.

2. Description of the Related Art

Among inkjet recording apparatuses that record an image by dischargingink droplets onto a recording medium such as paper, there is a so-calledscanning format inkjet recording apparatus where an inkjet recordinghead is disposed in a moving member such as a carriage and moving of theinkjet recording head in the direction orthogonal to the recordingmedium conveyance direction (main scanning) and moving of the recordingmedium (sub-scanning) are alternately conducted.

In this scanning format inkjet recording apparatus, the manufacturingyield of the inkjet recording head is high because the inkjet recordinghead is compact (as the requisite minimum configuration, it suffices ifthere is one nozzle for one recording head).

However, a limit has arisen in the pursuit of high productivity(conducting image recording on many recording media per unit time)because reciprocal movement (main scanning) of the inkjet recording headis indispensable at the time of image recording.

In order to realize high productivity, a so-called full line head formatinkjet recording apparatus has been proposed where a long inkjetrecording head, which can conduct image recording across a region thatis about the same as the width of the recording medium or larger, isfixed and image recording is conducted on the recording medium byconveying only the recording medium. With this format, high productivitycan be achieved in comparison to the scanning format because reciprocalmovement of the inkjet recording head is not necessary.

For example, Japanese Patent Application Laid-Open Publication (JP-A)No. 5-104705 discloses a recording apparatus disposed with full multiink-jet recording heads that can simultaneously conduct recording acrossthe entire width of the recording paper. Similarly, JP-A No. 6-126943discloses an ink-jet recording apparatus disposed with a so-called fullline type inkjet recording head.

Examples of specific configurations of such long inkjet recording headsinclude a configuration where, as described in JP-A No. 8-132700 forexample, the length is satisfied by a combination of plural recordingheads and a configuration where one recording head is integrally formed.However, advanced microfabrication technology is required in order toconfigure a long inkjet recording head with one member. In other words,because heads including several thousands to several tens of thousandsof nozzles must be manufactured as an integral part, sometimes the yieldbecomes poor.

The length of the recording head can be increased by joining togetherunit heads of a short length in the width direction of the recordingmedium, as described in JP-A No. 7-251505, JP-A No. 7-186386, JP-A No.10-95113, JP-A No. 2001-293871, JP-A No. 2001-301199, JP-A No.2002-103598 and JP-A No. 2002-59559, for example.

However, with this configuration, it becomes necessary to integrallyreplace the long recording head even when a drawback such as nozzleclogging arises in a specific unit head, so that costs necessary for thereplacement become extremely high.

SUMMARY OF THE INVENTION

The present invention has been made in light of the above-describedcircumstances. In accordance with a first aspect of the invention, thereis provided an inkjet recording apparatus including: conveyor devicesfor conveying a recording medium in a recording medium conveyancedirection generally orthogonal to a recording medium width direction;and plural head units that are disposed in a staggered manner so that animaginary line connecting the head units zigzags and extends in therecording medium width direction, with each head unit including pluralunit heads arranged in the recording medium conveyance direction.

These and other characteristics and advantages of the present inventionwill be apparent to those skilled in the art from the description of thepreferred embodiment of the invention as depicted in the attacheddrawings and from the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will be described in detailbased on the following figures, wherein:

FIG. 1A is a plan view showing the schematic configuration of an ink-jetrecording apparatus of an embodiment of the invention, and FIG. 1B is afront view of the same;

FIG. 2A is an explanatory diagram showing the relation between paperwidth and a recordable region of the inkjet recording apparatus of theembodiment, and FIG. 2B is an explanatory diagram showing the positionsof medium conveyor belts and belt recovery devices;

FIG. 3 is an explanatory diagram showing a unit head of the ink-jetrecording apparatus of the embodiment as seen from an ink dischargesurface side;

FIG. 4A is a plan view showing the schematic configuration of a modifiedexample of the inkjet recording apparatus, and FIG. 4B is a front viewof the same;

FIG. 5A is a plan view showing the schematic configuration of anothermodified example of the inkjet recording apparatus, and FIG. 5B is afront view of the same;

FIG. 6 is an explanatory diagram showing an ink supply system of theembodiment;

FIG. 7A is a bottom view of a recording head unit and shows the relationbetween the recording head unit and a cap member of the embodiment, andFIG. 7B is a front view of the same;

FIG. 8A is a front view showing an image recording time of the headrecovery device of the embodiment, FIG. 8B is a view showing a cappingtime, and FIG. 8C is a view showing a dummy jetting time;

FIG. 9 is a flow chart showing the sequence of ink droplet dischargeposition adjustment;

FIG. 10 is an explanatory diagram showing an example of a test patternrecorded in the ink droplet discharge position adjustment;

FIG. 11 is an explanatory diagram showing another example of a testpattern recorded in the ink droplet discharge position adjustment;

FIG. 12 is an explanatory diagram showing yet another example of a testpattern recorded in the ink droplet discharge position adjustment; and

FIG. 13 is an explanatory diagram showing another example of a testpattern recorded in the ink droplet discharge position adjustment.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1A and 1B, an inkjet recording apparatus 12 pertainingto an embodiment of the invention includes a paper supply tray 14 inwhich paper P (one example of a recording medium) is accommodated, arecording section 16 that records an image on the paper P supplied fromthe paper supply tray 14, and a paper discharge tray 18 thataccommodates the paper P on which an image has been recorded.

The paper P in the paper supply tray 14 is removed one sheet at a timeby a pickup roller (not shown) and conveyed to the recording section 16.In the drawings, arrow F represents the paper conveyance direction, andarrow W represents the paper width direction, which is orthogonal to thepaper conveyance direction.

As shown in FIG. 2A, the recording section 16 includes a recordableregion R1 of a width W1 that is substantially the same as or wider thana maximum width W0 of the paper P for which image recording is assumed.For example, assuming an A3 size (420 mm×297 mm) sheet of paper, themaximum width W0 thereof (length in the short direction) would be 297mm, so in the present embodiment, the width W1 of the recordable regionR1 would become 304.8 mm as described later.

The recordable region R1 in the width direction of the paper P can bedivided into plural individual recording regions R2. One recording headunit 22 is disposed in correspondence to and facing each recordingregion R2. Specifically, the recording head units 22 are positioned sothat recording head units adjacent to each other in the paper widthdirection alternate in the conveyance direction, i.e., they are disposedin a staggered manner.

Each recording head unit 22 is detachably attached to a housing (notshown) of the inkjet recording apparatus 12.

Below, the upstream-side recording head units 22 will be referred to asrecording head units 22A and the downstream-side recording head units 22will be referred to as recording head units 22B when it is necessary todistinguish the recording head units 22 between those at the upstreamside and those at the downstream side of the conveyance direction.

With respect to the paper P for which image recording has beencompleted, the regions recorded by the recording head units 22A and theregions recorded by the recording head units 22B are alternatelyarranged in the paper width direction.

As shown in FIG. 1B, a paper sensor 24A is disposed at the upstream sideof the recording head units 22A, and a paper sensor 24B is disposed atthe downstream side of the recording head units 22B. Each of the papersensors 24A and 24B detect the paper P and send that information to acontroller. A reading mechanism 34, which can read a test patternrecorded on the paper P, is disposed downstream of the paper sensor 24B.An imaging element such as a CCD that optically reads the test patterncan be used for the reading mechanism 34.

The recording head units 22 are configured so that plural unit heads 26having different ink discharge characteristics are arranged along thepaper conveyance direction.

As shown in FIG. 3, each unit head 26 includes a nozzle row 32configured by plural nozzles 28 formed along the paper width direction,and ink droplets corresponding to image information are discharged fromink discharge ports 30 at the ends of the nozzles 28.

As will be understood from FIG. 1A, in one recording head unit 22, theunit heads 26 are disposed so that both end positions of the nozzle rows32 overlap. Also, when seen in the paper conveyance direction, therecording head units 22A and the recording head units 22B are disposedso that they are aligned or overlap in the paper conveyance directionwithout gaps arising in the dots on the paper P resulting from the inkdroplets discharged from the unit heads 26. Thus, although the recordinghead units 22 record an image on the paper P in only the correspondingindividual recording regions R2 (widths W2), it becomes possible torecord an image across the entire width of the paper P with all of therecording head units 22. As described above, in a case where the unitheads 26 are disposed so that the dots from the unit heads 26 overlap inthe paper width direction, one of the two nozzles 28 corresponding tothe overlapping portion can be placed in disuse.

The aforementioned “ink discharge characteristics” refers to thecharacteristics of the ink droplets that are discharged, and include thecolor, droplet volume and discharge speed of the ink droplets, forexample. In the present embodiment, there are four unit heads 26 perrecording head unit 22, and the colors of yellow (Y), magenta (M), cyan(C) and black (K) are allocated in this order from the conveyancedirection upstream side. Thus, full color image recording becomespossible (below, Y, M, C or K will be added to the ends of referencenumerals when it is necessary to distinguish the unit heads 26 on thebasis of color). Of course, a configuration other than this is possible.For example, as shown in FIGS. 4A and 4B, there may also be two unitheads 26 per recording head unit 22, and different colors (e.g., blackand a highlight color) may be allocated to each unit head 26, so that atwo-color image is recordable. Also, as shown in FIGS. 5A and 5B, theremay be five or more unit heads 26 per recording head unit 22, so thatcolors other than Y, M, C and K (e.g., pale cyan or pale magenta) areadded and a configuration with higher color reproducibility is possible.Moreover, higher gradation can be obtained even with unit heads 26corresponding to the same colors by configuring the unit heads 26 sothat the ink droplet volumes are different.

As shown in FIG. 6, the ink is supplied to each unit head 26 through inksupply paths 36 from ink tanks (not shown). By disposing the ink supplypaths 36, which are shared by the plural unit heads 26, in this manner,the overall balance of the plural unit heads 26 (recording head units22) can be improved, which is preferable. Similarly, it is preferablefor a drive signal supply system for driving the unit heads 26 to beshared by the plural unit heads 26 so that the overall balance isimproved.

As mentioned above, each recording head unit 22 is configured byintegrating and unitizing plural unit heads 26 as one recording headunit. As shown in FIGS. 7A and 7B, each recording head unit 22 includesa recording head housing 40 that can retain the plural unit heads 26 atrelatively constant intervals. In a state where the unit heads 26 areattached to the recording head housing 40, the relative positionsthereof do not shift.

When seen in plan view, each recording head housing 40, which has apredetermined width W3 for correspondence (e.g., securement ofpressure-welded portion at a capping time) with electrical wiring, inksupply and later-described head recovery devices 70, protrudes furtheroutward in the paper width direction than the nozzle rows 32 of the unitheads 26. If these protruding portions are large, mutually adjacentrecording head housings 40 interfere with each other when the recordinghead units 22 are arranged in the paper width direction. In order toprevent this from happening, a countermeasure such as adding morerecording head units 22 in the medium conveyance direction to make threerows is conceivable to enable recording across the entire width of thepaper P, but in this case, the apparatus unavoidably becomes larger.

In the present embodiment, which eliminates this problem, the width W3of each recording head housing 40 is set to be equal to or less thantwice the length Ln (see FIG. 3) of the nozzle row 32 of the unit heads26. Thus, as shown in FIG. 2A, a so-called staggered disposition can beused where two rows configured by arranging recording heads at apredetermined pitch in the paper width direction are disposed in thepaper conveyance direction and the recording heads of one row and therecording heads of the other row are shifted at half pitch. Thus, therecording head housings 40 do not physically interfere with each other.Additionally, complete recording (printing) across the entire width ofthe paper P is possible even if the width of the paper P is quite wide.

As long as the above condition is satisfied, it is not necessary for therecording head housings 40 to be formed in rectangular shapes when seenin plan view; the recording head housings 40 can have polygonal shapesor shapes where protrusions are formed at the outer sides thereof.

In the present embodiment, the length of the nozzle row 32 of each unithead 26 is 25.4 mm (1 inch), for example. Two rows (in the paperconveyance direction) of six (in the paper width direction) recordinghead units 22 disposed with these unit heads 26 are disposed, for atotal of twelve recording head units 22. Overall, nozzle rows 32 of 25.4mm are arranged without gap when seen in the paper width direction, sothat the recordable region R1 has a width of 304.8 mm. The number ofrecording head units 22 can be appropriately set in accordance with therecordable range (length of nozzle row 32) per unit head 26. Forexample, in a case where the length of the nozzle row 32 is twice thelength described above (i.e., 50.8 mm (2 inches)), image recording of anentire A4 longitudinal direction (A3 short direction) becomes possibleby disposing three recording head units in each row in the paper widthdirection, for a total of six recording head units 22. Also, in a casewhere an image is to be recorded on paper having a width greater thanthis, the invention can have a configuration where all of the recordinghead units 22 are mounted on a carriage, these are integrally moved(main scanning), and main scanning and conveyance of the paper(sub-scanning) are alternately conducted. In this case, main scanningcan be conducted two times or four times to match the size of the paper,or so-called over-striking can be done. In this manner, the final imagerecording efficiency rises dramatically even with a configuration wherethe recording head units 22 are moved because the recording region perone-time main scanning is wide.

As shown in FIG. 1A, medium conveyor belts 38 are disposed in regions(called non-recording regions below) of the recordable region R1 wherethe ink droplets are not discharged from the recording head units 22(unit heads 26), i.e., at positions avoiding the locus of splattering ofthe ink droplets from the unit heads 26. Because the non-recordingregions are positioned in the paper width direction so as to alternatewith the recording head units 22, plural medium conveyor belts 38 aredisposed at equidistant intervals in the paper width direction.Additionally, because upstream-side medium conveyor belts 38A anddownstream-side conveyor belts 38B are disposed so as to be staggered bythe widths (W2) of the individual recording regions R2 in the paperwidth direction, the medium conveyor belts 38 are disposed in astaggered manner overall.

Thus, in the present embodiment, when the recordable region R1 is seenin the paper width direction, the recording head units 22A or therecording head units 22B are respectively disposed in the individualrecording regions R2 at constant periods (pitches). Moreover, the mediumconveyor belts 38A or the medium conveyor belts 38B are disposed atconstant periods in the non-recording regions. Thus, the recording headunits 22 and the medium conveyor belts 38 are alternately disposed.

Due to friction with the paper P, or by circulating (rotating) in apredetermined direction while electrostatically or non-electrostaticallyretaining the paper P, the medium conveyor belts 38 convey the paper P.Examples of non-electrostatic retention methods include suction andadhesion.

One drive roller 42 that spans the paper width direction is rotatablysupported at an unillustrated paper conveyance frame in the center ofthe paper conveyance direction of the recording section 16. Theupstream-side medium conveyor belts 38A and the downstream-side conveyorbelts 38B are alternately wound around and retained at the drive roller42.

One driven roller 44 that spans the paper width direction is disposed inboth the vicinity of the upstream end and the vicinity of the downstreamend of the paper conveyance direction and is rotatably supported viabearings at a driven roller frame 46 in the paper conveyance frame. Asshown in FIG. 1A, the medium conveyor belts 38A and the medium conveyorbelts 38B are wound around and retained at the corresponding drivenrollers 44.

The drive roller 42 is connected via a gear 48 (or directly) to a drivemotor 50. The drive motor 50 serves as a drive source for the mediumconveyor belts 38. All of the medium conveyor belts 38 can be circulated(rotatingly driven) at the same circulation speed by the rotation of thedrive roller 42 resulting from the drive of the drive motor 50. Thus,unevenness in the quality of a recorded image between the recording headunits 22A and 22B can be eliminated, and a high-quality image can beobtained. A stepping motor can be used as the drive motor 50, so thathighly precise paper conveyance control is possible, but the drive motor50 is not limited thereto.

An encoder 52 that outputs predetermined pulses in synch with therotation of the drive roller 42 is disposed at the drive roller 42. Adrive motor control device 54 controls the rotation of the drive motor50 on the basis of these output pulses, so that unevenness in therotation of the drive roller 42 arising from the output shaft of thedrive motor 50 or eccentricity of the gear 48 or the drive roller 42 canbe controlled within a fixed range.

The drive motor control device 54 is not limited to any format orstructure as long as it can execute the above-described control. Forexample, a device that conducts eccentricity control by reading, fromthe individual encoder signals at the time of rotation of the driveroller 42, differences with the ideal rotation of the drive roller 42,i.e., the eccentric error component, can be used.

As shown in FIG. 1B, the peripheral length La of the drive roller 42 ismade sufficiently long in comparison to the inter-nozzle distance Da ofthe unit heads 26 in the recording head units 22. Thus, even when thedrive roller 42 is rotating eccentrically, color shifts accompanyingperiodic fluctuations in the conveyance speed resulting from this, orshifts in the landing positions of the ink droplets between the unitheads, can be prevented. Namely, there are usually cases where the driveroller 42 rotates eccentrically, albeit slightly, even when it isattached to the paper conveyance frame with high precision. Even if thedrive roller 42 is rotated at a constant angle speed, periodicfluctuations arise in the circulation speed of the medium conveyancebelts 38 due to this eccentricity, and the conveyance speed of the paperP also periodically fluctuates. Here, in light of an optional place onthe paper P, the difference between the conveyance speed when the inkdroplets are discharged from the unit heads 26 of the recording headunits 22 at this optional place and the conveyance speed when the inkdroplets are discharged from different unit heads 26 of the samerecording head unit 22 becomes small. For this reason, shifts in thepositions at which the dots formed by the ink droplets from the unitheads 26 land also become small to the extent that they do not actuallybecome a problem. For example, in a case where affects resulting fromeccentric error of the drive roller 42, i.e., the maximum amount ofpositional fluctuations in the conveyance direction of each color of theink droplets discharged from the unit heads 26 is 100 μm, the error ofthe landing positions of the ink droplets from adjacent unit heads 26becomes 30 μm or less by making the inter-nozzle distance Da in therecording head units 22 to be 1/10 or less the period length La′, sothat an image where there are no practical problems can be obtained.

Also, because the period length of the drive roller 42 is sufficientlylong with respect to the inter-nozzle distance Db between the nozzles 28of the most downstream unit heads 26 of the recording head units 22A andthe nozzles 28 of the most upstream unit heads 26 of the recording headunits 22B, shifts in the dots resulting from the ink droplets from thesetwo groups of nozzles 28 can be eliminated.

As shown in FIGS. 8A to 8C (FIGS. 2B, 7A and 7B), head recovery devices70 corresponding to the recording head units 22 in a 1:1 ratio aredisposed at positions facing the recording head units 22 with theconveyed paper P sandwiched between the recording head units 22 and thehead recovery units 70, i.e., the head recovery devices 70 are disposedin regions where the medium conveyor belts 38A and 38B are not disposed.In FIGS. 8A to 8C, only the relation between the upstream-side drivenroller 44 and the drive roller 42 is shown, but head recovery devices 70are similarly disposed between the drive roller 42 and thedownstream-side driven roller 44. Also, the drawings seem to show thatthe recording head unit 22 is disposed with only one unit head 26, butin actuality plural unit heads 26 are disposed.

Each head recovery device 70 includes at least a cap member 72 thatopens towards the recording head unit 22 and a retention member 74 thatretains this cap member 72. The retention member 74 is lifted andlowered (so that the retention member 74 moves towards and away from therecording head unit 22) by an unillustrated lifting/lowering mechanism.Moreover, as needed, a suction device that sucks the inside of the capmember 72 is disposed.

As shown in FIG. 8B, in a state where the head recovery device 70 islifted, the cap member 72 tightly contacts and caps the recording headunit 22 so that the nozzle rows 32 (see FIG. 3) of all the unit heads 26are surrounded. Thus, the cap member 72 prevents inadvertent drying ofthe ink, prevents clogging of the nozzles 28 resulting from thick ink,and prevents deterioration of the ink. Also, in this state, a so-calledvacuum operation is conducted so that the ink is forcibly sucked fromthe nozzles 28 of the unit heads 26.

In contrast, in a state where the head recovery device 70 is lowered, asshown in FIG. 8A, the paper P is conveyed by the medium conveyor belts38A and 38B and becomes passable under the unit heads 26, so that imagerecording on the paper P can be conducted. Also, as shown in FIG. 8C,when the paper P is not present directly under the recording head units22 (e.g., between two sheets of paper P), so-called dummy jetting isconducted from the unit heads 26 so that the ink droplets thereof can bereceived by the cap member 72.

The lifting/lowering mechanism of the head recovery device 70 may bedisposed separately in each head recovery device 70 or may be disposedin common with plural head recovery devices 70. When thelifting/lowering mechanism is shared by the plural head recovery devices70, it can be configured so that the plural recovery devices 70 arefixed on a common base plate and the base plate itself is lifted andlowered.

Also, as mentioned above, it is preferable for the head recovery devices70 to be able to cap the recording head units 22, but there are alsocases where, depending on the configuration of the inkjet recordingapparatus 12, it suffices as long as they can receive the dummy-jettedink. Regardless of the configuration, disposing the head recoverydevices 70 in a 1:1 ratio with the recording head units 22 so that theycorrespond to all of the plural unit heads 26 configuring the recordinghead units 22 is preferable in terms of making the overall inkjetrecording apparatus 12 compact and inexpensive.

Because image recording across the entire width of the paper P ispossible by disposing the recording head units 22A and 22B so that theycover all of the individual recording regions, they may also have arandom disposition in the width direction of the paper P. However, inconsideration of the width of the head recovery devices 70, when therecording head units 22A and 22B are disposed at constant periods in thewidth direction of the paper P so that a certain amount of space isformed between the recording head units 22A or the recording head units22B, adjacent head recovery devices 70 do not interfere with each othereven if the width of the head recovery devices 70 is wide, andrestrictions in terms of disposition are reduced, which is preferable.

Similarly, it is preferable for the medium conveyor belts 38A and 38B tobe able to reliably convey the paper P and be disposed at positionsavoiding the locus of splattering of the ink droplets from the unitheads 26, but they may also have a random disposition in the widthdirection of the paper P. However, it is preferable to dispose themedium conveyor belts 38A and 38B at constant periods in the widthdirection of the paper P so that they can reliably convey the paper P.

The inkjet recording apparatus 12 records an image on the paper P on thebasis of an instruction from the controller (not shown).

This image recording operation will be described below.

In a state where there is no instruction from the controller, theink-jet recording apparatus 12 is in a standby state and each element isstopped. Each head recovery device 70 is lifted as shown in FIG. 8B sothat the cap member 72 tightly contacts the corresponding recording headunit 22 to prevent clogging of the nozzles 28 and deterioration of theink.

When there is an instruction from the controller to conduct imagerecording, the inkjet recording apparatus 12 lowers each head recoverydevice 70 as shown in FIG. 8A, so that the paper P can pass under therecording head units 22. In accordance therewith, the drive motor 50 isdriven, causing the drive roller 42 to rotate so that the mediumconveyor belts 38A and 38B circulate and are driven. At this time, asignal from the encoder 52 is received, eccentricity control isconducted and the drive motor 50 is rotated. In this manner, in a statewhere the circulation speed of the medium conveyor belts 38A and 38B isstable, the controller drives the pickup roller (not shown) to send thepaper P one sheet at a time from the paper supply tray 14 to therecording section 16.

When the paper sensor 24A detects the leading end of the paper P, thecontroller drives each unit head 26 on the basis of this detectionsignal so that the unit heads 26 discharge the ink droplets at apredetermined timing. Thus, ink droplets corresponding to imageinformation are successively discharged to predetermined positions onthe paper P from the unit heads 26 most upstream in the conveyancedirection, and image recording is conducted. Because the conveyance ofthe paper P in this state is conducted by the medium conveyor belts 38having a predetermined width in the paper conveyance direction and thepaper width direction, the medium conveyor belts 38 can secure flatnessof the paper P and stably convey the paper P with high conveyanceprecision.

At the point in time when discharge of the ink droplets from the headunits 26 most downstream in the conveyance direction is completed, imagerecording on the entire paper P is completed and the paper P isdischarged to the discharge tray 18. Then, when the number of sheets ofthe discharged paper P is counted and image recording of a predeterminednumber of sheets of the paper P is completed, the rotation of the drivemotor 50 is stopped and the circulation of the medium conveyor belts 38Aand 38B is also stopped. The number of sheets of the discharged paper Pcan be detected by the paper sensor 24B detecting the trailing ends ofthe sheets of the paper P.

As mentioned above, when images are to be recorded on plural sheets ofthe paper P, dummy jetting can be conducted in the empty spaces betweenthe sheets of the moving paper P. The head recovery devices 70corresponding to the unit heads 26 ordinarily face the recording headunits 22, and when dummy jetting is to be conducted, it is not necessaryto relatively move the unit heads 26 or the head recovery devices 70 inthe paper moving direction. Thus, the structure of the inkjet recordingapparatus 12 can be simplified and made compact. Also, the mediumconveyor belts 38A and 38B are disposed in the non-recording regions, sothat ink discharged in the dummy jetting does not inadvertently adhereto the medium conveyor belts 38A and 38B. Thus, it is possible toconduct dummy jetting in the regions between the sheets of paper P whileconducting image recording, and high productivity can be obtained.

Thereafter, the controller causes the head recovery devices 70 to belifted, so that the unit heads 26 are capped by the cap members 72.Thus, the series of image recording operations is completed.

In this manner, the inkjet recording apparatus 12 of the presentembodiment can conduct image recording across the entire width of thepaper P simply by conveying the paper P, without having to move therecording head units 22A and 22B (in the paper width direction), andproductivity becomes higher.

Moreover, in the present embodiment, each recording head unit 22 isunitized, so that the recording head units 22 can be individuallyreplaced when drawbacks such as so called clogging arises in a specificnozzle of the unit heads 26. In contrast, when the inkjet recordingapparatus has a configuration where plural unit heads 26 are unitized inthe paper width direction, as will be understood from FIGS. 1A and 1B,the number of unit heads 26 to be replaced increases, which leads to anincrease in cost, because six (depending on the case, twelve) unit heads26 are unitized in the paper width direction. For example, in a casewhere 1200 dpi unit heads are used to enable image recording on a 12inch wide sheet of paper, 14400 nozzles per color are arranged in thewidth direction of the paper. When a drawback arises in only some ofthese nozzles, replacing the integrated unit heads across the widthdirection leads to an increase in cost. However, in the presentembodiment, costs necessary for replacement become lower because itsuffices to replace only the recording head unit 22 to which the unithead 26 including the nozzle in which the drawback has arisen isattached.

In this manner, in a configuration where the recording head units 22(unit heads 26) are replaceable, there are cases where attachmentprecision of the unit heads 26 after replacement cannot be highlydemanded. For example, sometimes the positional precision between theunit heads 26 is 100 μm or less due to error in the fixing time of therecording head unit 22. In a case where an image with a resolution of1200 dpi is to be recorded, it is preferable to keep this error to about10 to 20 μm.

The inkjet recording apparatus 12 can adjust the discharge positionsbetween the unit heads 26 and inside the unit heads 26 by the sequenceshown in FIG. 9.

First, in step 102, a predetermined test pattern is recorded on thepaper P. Although it suffices for the test pattern to be one where thelanding positions of the ink droplets discharged from the nozzles 28 ofthe unit heads 26 can be precisely detected, it is preferable for thetest pattern to be one where, for example, dots are arranged in a matrixon the paper P. FIGS. 10 to 12 show test patterns TP configured by amatrix M1, which is formed by a specific unit head 26, and a matrix M2,which is formed by a unit head 26 of the same color adjacent in thepaper width direction. In FIGS. 10 to 12, the number of dots configuringthe matrixes is fewer than in actuality. In the actual matrixes, thesame number of dots as the nozzles configuring the nozzle row 32 arearranged in the paper width direction. Also, dots of a numbercorresponding to the time (discharge frequency) when the ink dropletsare discharged are arranged in the paper conveyance direction.

In step 104, the test pattern TP is read by the reading mechanism 34,and the positions of the dots in the recording head units 22 aredetected. With respect to the test pattern TP, there are cases where thematrix M1 and matrix M2 are shifted in the paper conveyance directionper unit head 26 (see FIG. 10), cases where the matrixes are shifted inthe paper width direction, cases where the matrixes overlap in the paperwidth direction (see FIG. 11), and cases where (large) gaps between thematrixes arise in the paper width direction (see FIG. 12). Regardless ofthe case, in step 106, the discharge positions between the unit heads 26are adjusted. The adjustment of the discharge positions can be done bychanging, per recording head 26, the recording timing, i.e., the timingat which the ink droplets are discharged, when the dots are shifted inthe paper conveyance direction. Also, in a case where the dots overlapin the paper width direction, the adjustment can be done so that the inkdroplets are not discharged from the nozzles 28 corresponding to theoverlapping portion. In a case where a gap in the paper width directionarises between the dots, ink droplets are discharged from the non-usednozzles 28 corresponding to the gap portion (in consideration of thispoint, it is preferable to sufficiently secure the length of the nozzlerows 32 so that non-used nozzles can be present in advance at both endportions of the nozzle rows 32). In this manner, in a state where thedischarge positions between the unit heads 26 have been adjusted, thecounter representing discharge abnormalities per unit head 26 is resetin step 108, so that n=0.

Next, the test pattern is recorded again on the paper P in step 110. Instep 112, variations in the dots in the unit heads 26 are detected, andit is determined in step 114 whether or not these variations are withinan allowable range. Namely, during inkjet recording, as shown in FIG.13, there are cases where there are abnormalities in the dischargedirection of the ink droplets resulting from the adherence of foreignmatter to the nozzles 28 or where dots are missing due to clogging. Whenthe variations are within the allowable range, the processing ends. Whenit is determined that the variations exceed the allowable range, 1 isadded to the numerical value of the counter in step 116.

In step 118, it is determined whether or not the numerical value of thecounter has reached a predetermined value (in FIG. 9, the value is setto “5”). When the numerical value of the counter has not reached thepredetermined value, predetermined maintenance processing is conductedin step 120, and the discharge state is recovered. This maintenanceprocessing includes cleaning of the ink discharge surface using anunillustrated wiping member and suction (vacuum operation) of the inkfrom the nozzles. The vacuum operation is conducted in a state where, asshown in FIG. 8B, the head recovery devices are lifted and the unitheads 26 are capped by the cap members 72. After this maintenance hasbeen conducted, the processing returns to step 110 and the sameprocessing is conducted thereafter.

When it is determined in step 118 that the numerical value of thecounter has reached the predetermined value, it is conceivable that theunit heads 26 have failed and replacement thereof is necessary. Thus, instep 122, failure display where the fact that a specific recording headunit 22 (or unit head 26) has failed is displayed on a display unit suchas a display panel 56, the user is prompted to replace the failedrecording head unit 22 (or unit head 26), and processing ends. Even whenfailure display is done on the display unit, there are cases where thefailure does not substantially become a problem depending on the type ofimage to be recorded. Also, in actual replacement, sometimes it takestime to procure a new recording head unit 22. Thus, it is preferable toenable continuous image recording by ensuring that the operation of theinkjet recording apparatus 12 is not completely stopped.

The above-described sequence includes a first portion where dischargeposition adjustment between the unit heads 26 is conducted (steps 102 to106) and a second portion where discharge position adjustment in theunit heads 26 is conducted (steps 108 to 122), but simply the firstportion may be conducted when the discharge position adjustment betweenthe unit heads 26 is to be conducted. Similarly, simply the secondportion may be conducted when the discharge position adjustment in theunit heads 26 is to be conducted.

Because the invention has the above-described configuration, productionefficiency is raised and costs necessary to replace recording heads canbe reduced.

As can be seen from the above description, in the inkjet recordingapparatus according to the present invention, the plural recording headsare disposed in correspondence to plural individual recording regionsdivided in the recording medium width direction, so that overall, theinkjet recording heads can be made to correspond to the entire width ofthe recording medium. Thus, image recording along the entire width ofthe recording medium can be conducted by conveying the recording mediumwith the conveyance device. High productivity can be obtained because itis not necessary to move (main scan) the recording head units. Yieldalso becomes high because it is not necessary to make the unit headsconfiguring the recording head units long.

Moreover, the recording head units include plural unit heads that havedifferent ink discharge characteristics and are unitized along theconveyance direction, and the recording head units can be replaced inrecording head unit units, whereby costs necessary to replace therecording heads becomes lower.

With respect to the unit heads, “different ink dischargecharacteristics” widely includes discharging ink droplets of differentcolors, ink droplets of different droplet volumes, and that thecharacteristics of the ink droplets that are actually discharged aredifferent. For example, it becomes possible to record a so-called fullcolor image by configuring one recording head unit with four (or more)head units and configuring the head units to be able to discharge inkdroplets of at least yellow (Y), magenta (M), cyan (C) and black (K).

The “recording medium” serving as the target of image recording in theinkjet recording apparatus of the present invention widely includestargets to which the inkjet recording apparatus discharges the inkdroplets. Also, dot patterns on the recording medium obtained as aresult of the ink droplets adhering to the recording medium are widelyincluded in the “image” or “recording image” obtained with the recordingapparatus of the present invention. Thus, the inkjet recording apparatusof the present invention is not limited to an apparatus used to recordcharacters and images on recording paper. Of course, recording paper andOHP sheets are included in the recording medium, but in addition tothese, substrates on which a wiring pattern is formed are also included.Also, included in the “image” are not only common images (characters,illustrations, photographs, etc.) but also the aforementioned wiringpattern, three-dimensional objects and organic thin films. The liquid tobe discharged is also not limited to color ink. For example, the inkjetrecording apparatus of the present invention can be applied to commondroplet jetting devices used for various industrial purposes, such asthe manufacture of color filters for displays conducted by dischargingcolor ink onto a polymer film or glass, the formation of bumps for partspackaging conducted by discharging molten solder onto a substrate, theformation of EL display panels conducted by discharging an organic ELsolution onto a substrate, and the formation of bumps for electricalpackaging conducted by discharging molten solder onto a substrate.

1. An inkjet recording apparatus comprising: conveyor devices forconveying a recording medium in a recording medium conveyance directiongenerally orthogonal to a recording medium width direction; and pluralhead units that are disposed in a staggered manner so that an imaginaryline connecting the head units zigzags and extends in the recordingmedium width direction, with each head unit including plural unit headsarranged in the recording medium conveyance directions, wherein theconveyor devices include conveyance units for conveying the recordingmedium disposed in empty regions between the head units that areadjacent in the recording medium width direction.
 2. The inkjetrecording apparatus of claim 1, wherein each unit head includes pluralink discharge nozzles arranged in the recording medium width direction.3. The inkjet recording apparatus of claim 2, wherein when Ln representsan inter-nozzle distance between the nozzles at both end sides of theunit heads in the recording medium width direction and W3 represents asubstantially outer dimension of the head units in the recording mediumwidth direction, W3<2×Ln.
 4. The inkjet recording apparatus of claim 1,wherein the plural unit heads of one head unit have mutually differentink discharge characteristics.
 5. The inkjet recording apparatus ofclaim 4, wherein the ink discharge characteristics include ink colorsset per unit head.
 6. The inkjet recording apparatus of claim 1, whereineach head unit includes four unit heads where inks of yellow (Y),magenta (M), cyan (C) and black (K) are allocated.
 7. The inkjetrecording apparatus of claim 1, wherein each head unit is detachablyindependent from the other head units.
 8. The inkjet recording apparatusof claim 1, wherein the plural head units are included in a head unitrow at the upstream side of the recording medium conveyance directionand a head unit row at the downstream side of the recording mediumconveyance direction.
 9. The inkjet recording apparatus of claim 8,wherein each of the head unit rows is configured by the head unitsarranged in the recording medium width direction with predeterminedintervals disposed therebetween.
 10. The inkjet recording apparatus ofclaim 1, further comprising a reading device that can read apredetermined test pattern recorded by the head units, and a displaydevice that can display, on the basis of the reading result, at leastone of a head unit and a unit head that is to be replaced.
 11. Theinkjet recording apparatus of claim 1, wherein each of the conveyanceunits includes a conveyor belt.
 12. The inkjet recording apparatus ofclaim 1, further comprising plural head recovery devices correspondingto the head units.
 13. The inkjet recording apparatus of claim 12,wherein each of the head recovery devices includes a cap member that cancover all of the unit heads of the corresponding head units.
 14. Theinkjet recording apparatus of claim 13, wherein each of the cap membersis separably for movable the covering with respect to the correspondinghead units.
 15. An inkiet recording apparatus comprising: plural headunits that are disposed in a staggered manner so that an imaginary lineconnecting the head units zigzags and extends in a first direction;plural head recovery devices that are disposed facing the head units;and plural conveyance units for conveying a recording medium in a seconddirection intersecting the first direction, the conveyance units beingdisposed adjacent to the head recovery devices.
 16. The inkjet recordingapparatus of claim 15, wherein at least one of the conveyance units isdisposed between the head recovery devices.